Radiation counting means



F. w. WIECHERING 3,019,363

RADIATION COUNTING MEANS Filed 001;. 25, 1959 Jan. 30, 1962 NON-MEMLL/C COA T/NG GH5EOU5 F/LL/NG PR/NC/P/ILLY 0F NEON AND A SMALL AMOUNT OF 5,5 A'NO GL INVENTQR.

tates This invention relates, generally, to radiation counters and it has particular relation to such counters having a self-quenching gaseous filling.

The quenching agents which are normally used in Geiger-Muller counters are organic gases or halogen gases. The organic quenched Geiger-Muller counters have a limited life time in the range of counts due to the dissociation of the organic molecules. The halogen quenched Geiger-Muller counters have a much longer life time which is limited only by the possible absorption of the halogen molecules on the cathode. The difference in the counting rate between organic Geiger-Miiller counters and halogen quenched Geiger-Muller counters of the same size and in the same radiation field is significant. In accordance with the present invention the best operational features found in organic and halogen quenching agents are combined to provide an improved radiation counter.

Among the objects of this invention are: To improve the operational and life characteristics of self quenching Geiger-Muller counters; to provide a new gaseous filling for Geiger-Miiller counters; to employ for this purpose a filling principally of an inert gas in combination with an admixture of a halide and a halogen gas; to use for the halide, substantially pure silicon tetrailuoride, and for the halogen, chlorine.

Other objects of this invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the nature and scope of this invention reference can be had to the following detailed description, taken together with the accompanying drawing, in which the single FIGURE illustrates diagrammatically the conventional form of a Geiger- Miiller counter provided with a gaseous filling in accordance with the present invention.

Referring now particularly to the drawing, it will be observed that the reference character 10 designates generally a Geiger-Miller counter which is illustrated in a diagrammatic form. It will be understood that the mechanical details of construction may be varied as desired by one skilled in the art.

The Geiger-Muller counter 10 includes an envelope 11 which is formed of material such as glass, metal or plastic. It is elongated and cylindrical in shape but it is not necessarily so limited and is provided intermediate its ends with a cathode 12 in the form of a non-metallic coating, such as stannic oxide or other metal oxides, or a metal cathode which may be or not integral with the counter shell or envelope 11.

A conductor 13 extends through the envelope 11 and provides a connection to the cathode 12. Centrally located with respect to the cylindrical cathode 12 and extending along the longitudinal axis therefore is an anode 14 in the form of a wire which is provided with a conductor 15 that extends through the envelope 11. It will be understood that a suitable potential is applied between the conductors 13 and 15 in accordance with conventional practice.

Within the envelope 11 there is provided a gaseous filling that is indicated at 16. The gaseous filling consists of the noble gas and the quenching agent. With a suitable potential and in a radiation field this gas filled apparatus or counter It) performs as a self-quenched Geiger-Muller counter. Bet-2 gamma and X-ray radiation can be measured. Alpha radiation can be measured by using a suitably thin window for the counter 10.

The gaseous filling 16 consists principally of an inert gas such as helium, neon, argon, krypton or xenon or various mixtures of these mentioned gases. The quenching agent consists of a mixture of an organic or inorganic halide with one of the halogen gases.

As a specific example of the composition of the gaseous filling 16 for the Geiger-Miiller counter 10, the inert filling gas is neon and the added quenching agent is a mixture of the inorganic halide gas (silicon tetrafluoride) and the halogen gas (chlorine). In millimeters of mercury these gases are employed in the following partial pressures and percentages Mm. Neon gas 700 Quenching mixture (SiF -l-Cl 6 1 Of this quenching admixture the amount of Cl: is 4%.

By partial pressures of millimeters of mercury the re lationship can be expressed as follows:

The relative percentages of these gases by pressure are as follows:

C1 gas 0.034% Purified SiF, gas 0.816% Neon gas Remainder While optimum results are obtained using 4% C1 as set forth in the foregoing example, the C1 can range from 3% to 5%. The higher the C1 the lower the counting rate.

It is pointed out that silicon tetrafluoride gas obtained commercially is purified for use in the counter 10 by a purification process which involves the lowering of the temperature of the gas through repeated phases and then drawing off the impurities While subjecting the system to pressure less than atmospheric pressure. The purified silicon tetrafiuoride gas is solidified with the required amount of chlorine under suitable conditions of temperature and pressure. The sublimation of the silicon tetrafluoride and chlorine is allowed to proceed to the gaseous state where it is combined with the inert gas, such as neon, to provide the gaseous filling 16 for the Geiger- Miiller counter 10.

The Geiger-Muller counter 16 is provided with the gaseous filling 16, formed principally of neon, and having an admixture of small amounts of silicon tetrafiuoride and chlorine has numerous advantages. Among them are:

(1) Nearly unlimited lifetime.

(2) A gas efiiciency approaching (3) An operating range from -60 C. to +220 C.

(4) Little damage when excessive voltage is applied between the conductors 13 and 15.

(5) Quick recovery after glow discharge.

(6) Substantially no photosensitivity.

(7) Can be used with neon gas for a wide range of pressures up to atmospheric and still provide the desired operating characteristics.

(8) The gaseous filling does not react with the stannic oxide coating forming the cathode 12.

(9) A long plateau with a very small slope.

(10) A wide range of starting potential dependent on the percentage of the quenching agent.

The Geiger-Miiller counter 10 employing the gaseous filling 16 described herein has been operated at a counting rate of 2.6 10 counts per day or more.

Operation of this counter in long life tests in the temperature range from -60 C. to +220 C. showed there was no significant change in the plateau characteristics and that there was no damage to the cathode 12 or the anode 14. Examination of the photosensitivity over a frequency range of 2,500 A. to 40,000 A. showed that the Geiger-Muller counter 10 was free from photosensitivity. The background characteristics were equal to those of good organic quenched Geiger-Muller counters. The length of the plateau was found to be of the order of 300 volts. The slope of these plateaus was of the order of 2% or less.

When bromine or iodine is used in lieu of chlorine, higher percentages thereof are necessary. A lower starting potential is required for these additives than for chlorine.

What is claimed as new is:

1. A Geiger-Muller counter comprising, in combination, an envelope, a pair of electrodes therein, and a gaseous filling in said envelope consisting essentially on the basis of relative percentages by pressure of neon containing about 0.034% chlorine and about 0.816% silicon tetrafiuoride.

2. A Geiger-Muller counter comprising, in combination, an envelope, a pair of electrodes therein, and a gaseous filling in said envelope consisting essentially of the following gases in proportions giving substantially the following partial pressures in millimeters of mercury:

Gas: Partial pressure Neon 700 Chlorine 0.24 Silicon tetrafluoride 5.76

3. As a new composition of matter neon containing on the basis of relative percentages by pressure about 0.034% chlorine and about 0.816% silicon tetrafluoride.

No references cited. 

1. A GEIGER-MULLER COUNTER COMPRISING IN COMBINATION AN ENVELOPE, A PAIR OF ELECTRODES THEREIN AND A GASEOUS FILLING IN SAID ENVELOPE CONSISTING ESSENTIALLY ON 